Crosstalk suppression in wireless testing of semiconductor devices

ABSTRACT

An integrated circuit integrated on a semiconductor material die and adapted to be at least partly tested wirelessly, wherein circuitry for setting a selected radio communication frequencies to be used for the wireless test of the integrated circuit are integrated on the semiconductor material die.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/006,942,filed Jan. 14, 2011, which application is a division of application Ser.No. 12/037,319, filed Feb. 26, 2008, which application claims thepriority benefit of Italian Patent Application No. MI2007A000386, filedFeb. 28, 2007, entitled Crosstalk Suppression In Wireless Testing OfSemiconductor Devices, which applications are hereby incorporated byreference to the maximum extent allowable by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and systems for testingIntegrated Circuits (ICs).

2. Discussion of the Related Art

ICs are typically manufactured many at a time in the form of dies on asemiconductor material wafer. After manufacturing, the semiconductorwafer is diced, so as to obtain a plurality of IC chips.

Before being shipped to the customers, and installed in variouselectronic systems, the ICs need to be tested to assess theirfunctionality, and in particular ensuring that they are not defective.In particular, during the test, information regarding global or localphysical faults (such as undesired presence of short circuits andbreak-down events) and more generally the operation of each die, can bedetected (for example, by checking the waveform of one or more outputsignals of each die) so that only the dies that meet predeterminedrequirements, move to the subsequent manufacturing phases (such as leadbonding, packaging and final testing).

According to a known testing technique, the IC dies are tested beforethe semiconductor wafer is diced into the individual chips. The testconducted at the wafer level is referred to as “Wafer Sort”.

For example, in case of non-volatile semiconductor memory devices (suchas Flash memories) a test known as EWS (Electrical Wafer Sort) isperformed on each die wherein the memory device is formed, in order toverify the correct operation thereof.

For performing the test, a tester is used which is coupled to thesemiconductor wafer containing the dies to be tested, by means of aprobe card which is used for interfacing the semiconductor wafer to thetester.

The tester is adapted to manage signals that are employed for performingthe test. Hereinafter, such signals will be referred as test signals andinclude data signals which are generated by the tester and which aresent to each die to be tested by the probe card, and response signalswhich are generated by each die in response to the received datasignals. The response signals are sent by each die to the tester, whichprocesses them to derive an indication of the proper or improperoperation of the die under test.

Often (for example during EWS), probes are employed wherein theelectrical coupling of the probe card with the dies to be tested,necessary for achieving the signal exchange, is accomplished through aphysical contact. For this purpose, the probe card consists of a PCB(Printed Circuit Board), which is connected to a large number (of theorder of some thousands) of mechanical probes, which are adapted tophysically contact input/output contact pads of each die to be tested.

However, this type of test system has several limitations; for example,there is the risk of damaging the contact pads of the die under test;also, it has a reduced parallel testing capacity: indeed, when more dieshave been tested at the same time, the number of mechanical probessignificantly increases, and it may happen that the electrical contactsbetween the pads and the mechanical probes are not good and electricaldiscontinuities may take place.

Moreover, when the contact pads are very close to each other, it is verydifficult to ensure a good physical contact of the mechanical probeswith the pads. Such problem is emphasized when the pads have are smallin size and/or a large number thereof is present on each die.

In addition, the mechanical probes are very expensive, and thisnegatively contributes to the increase of the overall cost of the testsystem, and eventually of the ICs.

In an alternative, the test signals are, fully or at least in partwirelessly exchanged between the probe card and the dies to be tested,through wireless circuits embedded in the probe card. Typically, eachtesting site of the wireless probe card comprises at least onetransceiver circuit and one or more micro-antennas which are able tocommunicate with the die through wireless communication, at radiofrequency, with corresponding micro-antennas and transceiver circuitsintegrated on the dies, so as to establish a wireless bi-directionallink between the tester and the die under test. In such a way, awireless test is performed, and the mechanical probes are, fully or inpart, eliminated.

A drawback of this solution is that when two or more dies are tested atthe same time, there is a cross-talk between the test signalscorresponding to different dies. This problem is particularly felt whenthe dies which have to be tested at the same time are close to eachother, possibly adjacent.

In order to avoid cross-talk phenomena, the dies of the semiconductorwafer have to be tested one at a time, but this significantly increasesthe overall testing time.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, different radiocommunication frequencies are used for simultaneous wireless testing oftwo or more dies.

Particularly, the present invention provides a solution as set out inthe independent claims.

Advantageous embodiments of the invention are provided in the dependentclaims.

In detail, an aspect of the present invention provides an integratedcircuit integrated on a semiconductor material die and adapted to be atleast partially tested wirelessly, wherein means for setting at least aselected radio communication frequency to be used for the wireless testof the integrated circuit are integrated on the semiconductor materialdie.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, and advantages of the present invention willbe made apparent by the following detailed description of an embodimentthereof, provided merely by way of non-limitative example, descriptionthat will be conducted making reference to the attached drawings,wherein:

FIG. 1 schematically shows a block diagram of a test system according toa an embodiment of the present invention;

FIG. 2 schematically shows a communication frequency selector of FIG. 1,according to an embodiment of the present invention;

FIG. 3 schematically shows a communication frequency selector, accordingto another embodiment of the present invention;

FIG. 4 schematically shows a transceiver circuit adapted to cooperatewith a communication frequency selector, for changing the radiocommunication frequency, according to an embodiment of the presentinvention; and

FIG. 5 schematically shows a cross-sectional view of a test equipmentwherein the test system according to the present invention is used.

DETAILED DESCRIPTION

Throughout the following description, identical or similar elements inthe drawings are denoted by same reference numerals.

Referring to FIG. 1, a block diagram of a test system 100 according toan embodiment of the present invention is schematically shown. The testsystem 100 is adapted to wirelessly testing a plurality (for example,hundreds) of IC dies 105 belonging to a semiconductor wafer 110.

The specific type of IC 115 integrated on the dies 105 is not alimitation of the present invention; in particular, and merely by way ofexample, the ICs 115 may be or include memory devices, microprocessorsor microcontrollers, digital logic circuits, Application SpecificIntegrated Circuits (ASICs).

For testing the dies 105 in order to assess their functionality, thetest system 100 comprises a tester 120, which is adapted to generatetest signals to be fed to the ICs 115 integrated on the dies 105; thetester 120 is coupled to a wireless probe card 125, which is adapted tobe fed by the tester 120 (through wireline and/or wireless electricalsignal distribution means 130 (which may be or include electricalcables, conductive lines or tracks, a radio link or an optical link)with the test signals, and the power supply necessary for its operation;the wireless probe card 125 is employed for interfacing the tester 120with each die 105 on the wafer 110.

The wireless probe card 125 comprises a control circuit 135 adapted tomanage the test signals exchanged with the tester 120, and a testingsection 137 comprising a plurality of wireless units 140, each of whichis adapted to wirelessly communication with a corresponding wirelesscommunication unit 145 provided in each die 105. In other words, each ofthe wireless units 140 of the testing section 137 of the wireless probecard 125 is adapted to establish a one-to-one communication relationshipwith a corresponding wireless communication unit 145 provided on one ofthe dies 105 of the semiconductor wafer 110 to be tested. It is pointedout that in some embodiments of the invention, the plurality 137 ofwireless units 140 of the wireless probe card 125 may include a numberof wireless units 140 equal to the number of dies 105 of the wafer 110to be tested (in which case, all the dies of the wafer can in principlebe tested in parallel); however, in alternative embodiments of theinvention, the number of wireless units 140 may be lower than the numberof dies 105 of the wafer 110 (in which case, groups of dies of the waferare tested in parallel), or the number of wireless units 140 may be evengreater than the number of dies 105 of the specific wafer under testing(in which case, only a subset of the wireless units 140 are used fortesting the whole wafer).

The tester 120 and the control circuit 135 of the wireless probe card125 may communicate through a tester interface input/output circuit 150.The control circuit 135 comprises for example a data processor 155 whichcontrols overall the operation of the wireless probe card 125, and whichoperates under the control of a software stored in a storage unit 160.

More in detail, each wireless unit 140 includes at least one transceivercircuit (or transponder) 165, which is coupled to at least one antenna170. Similarly, each wireless communication unit 145 on the die 105includes at least one transceiver circuit (or transponder) 175, which iscoupled to at least one micro-antenna 180. The transceiver circuits 165,with the associated antennas 170, and the transceiver circuits 175, withthe micro-antennas 180, are adapted to establish a wirelessbi-directional link between the wireless probe card 125 and each die 105of the wafer under test 110.

The power supplies necessary for the operation of the ICs may also bewirelessly transferred to the dies 105 under test from the wirelessprobe card 125, or it is possible to use other methods, such as probes,to supply power to dies 105.

The generic transceiver circuit 165 encodes the test signals receivedfrom the tester 120 and transmits them to the generic transceivercircuit 175 on a die 105 using any suitable coding and radio frequencymodulation scheme. Examples of radio frequency modulation schemesinclude Amplitude Modulation (AM), Frequency Modulation (FM), Pulse CodeModulation (PCM), phase modulation or any combination thereof. Thespecific coding and modulation scheme is not per-se limitative for thepresent invention.

Then, the transceiver circuit 175 receives, demodulates and decodes thetest signals, and the test signals are then used to test the ICintegrated on the die 105; response signals are generated in response tothe test signals: the response signals are encoded, modulated andtransmitted by the transceiver circuit 175 to the wireless probe card125, where the transceiver circuit 165 performs a demodulation anddecoding, and the response signals are then sent to the tester 120,which processes them to assess the functionality of the IC integrated onthe die 105 under test.

According to an embodiment of the present invention, in order to testmultiple dies in parallel without incurring in cross-talk problems,different radio communication frequencies are used by the wireless probecard 125 for communicating with the different dies 105 to be tested inparallel.

To this purpose, in an embodiment of the present invention, integratedin the generic die 105 is a radio frequency selector 185, whichdetermines the generic radio frequency to be used by the wirelesscommunication unit 145 integrated on the die to communicate with thewireless probe card 125. In particular, the radio frequency selector 185is operatively coupled to the transceiver circuit 175, which sets thegeneric radio communication frequency according to the indicationsprovided by the radio frequency selector 185. In this way, thetransceiver circuit 175 is tuned on the same frequency used by thecorresponding wireless unit 140.

The radio frequency selectors 185 integrated on each die 105 allowsetting different radio communication frequencies for each die 105 to betested in parallel with other dies of the wafer 110. In such a way, twoor more, possibly all the dies 105 of the semiconductor wafer 110 can betested at the same time so avoiding cross talk among the test signals.

Alternatively, it may be provided that only adjacent dies 105 on thewafer 110 use differentiated radio communication frequencies. Forexample, a radio frequency pattern may be defined, according to whichdifferent radio communication frequencies are set for groups of two ormore adjacent dies 105 on the wafer 110. The radio frequency selectors185 integrated in the dies 105 follow the predefined pattern of radiofrequencies on the semiconductor wafer 110.

Referring to FIG. 2, an implementation of the radio frequency selector185 of FIG. 1 is shown, using fuses to set the desired radiocommunication frequencies.

The radio frequency selector 185 comprises a circuit having a pluralityof circuital branches 210, each of which is adapted to provide one bitof a binary code corresponding to the desired radio communicationfrequencies to be used by the corresponding die 105 for communicatingwith the wireless unit 140 of the wireless probe card 125. For thispurpose, at least one programmable element, such as a fusible link FL,is provided in each circuital branch 210. The radio frequency selector185 can be programmed by selectively burning the fusible links FL, so asto store in the radio frequency selectors 185 the binary codescorresponding to the selected radio communication frequencies.

In greater detail, in an embodiment of the present invention eachfusible link FL has a first terminal connected to a power supplydistribution line DL distributing the power supply, and a secondterminal coupled to a first terminal of a respective pull-down circuit215 (for example including one or more resistors or transistors, e.g.MOSFETs) which has the second terminal connected to a ground voltagedistribution line. The second terminal of the fusible link FL providesan output voltage signal Vout whose value is indicative of the bitstored in the circuital branch 210. For example, the bit has a logiclevel “0” when the output voltage signal Vout reaches a low level (inthe example at issue, ground), whereas the bit has a logic level “1”when the output voltage signal reaches a high level (in the example atissue, the power supply).

Before performing the test on the dies 105 of the semiconductor wafer110, the radio communication frequencies of the different dies 105 areset by programming the radio frequency selector 185. In particular,considering the generic circuit branch 210 (similar considerationsapplies to the other circuit branches 210 of the radio frequencyselector 185), after manufacturing of the wafer 110 the fusible link FLis conductive and the output voltage signal Vout reaches approximatelythe supply voltage (thus, the corresponding bit in the binary code is“1”). During the programming phase of the radio frequency selectors 185,the fusible link FL may be burned (for example, electrically, or usinglaser or other suitable methods), becoming (in this particularembodiment) essentially an open circuit, in which case the outputvoltage Vout reaches approximately the ground (thus, the correspondingbit in the binary code is “0”).

By performing similar operations on the other circuit branches 210, thebinary code corresponding to the desired radio communication frequenciesis stored in the radio frequency selector 185.

On the side of the test equipment, the tester 120 sets the proper radiocommunication frequencies in transceiver circuits 165 of each wirelessunit 140, so that each wireless unit 140 can wirelessly communicate witha wireless communication unit 145 integrated on a corresponding die 105to be tested.

Afterward, the semiconductor wafer 110 is brought in close proximity(such as less than 100 μm) of the wireless probe card 125, so that thedies 105 are close to respective wireless units 140 which are integratedon the wireless probe card 125. The IC integrated on each die 105 isthen tested based on test signals that are generated by the tester 120and which are wirelessly exchanged by the wireless unit 145 and acorresponding wireless unit 140.

In response to the received test signals, each IC 115 performs apredetermined test, and generates the response signals, which arewirelessly transmitted to the corresponding wireless unit 140; theresponse signals are sent to the tester 120, which processes them inorder to assess whether the ICs 115 integrated on the dies 105 operateproperly.

Referring to FIG. 3, an implementation of the radio frequency selector185 according to a second embodiment of the present invention is shown.In this embodiment, the radio frequency selector 185 includes anon-volatile storage area 305. In the example at issue, the non-volatilestorage area 305 includes non-volatile memory cells MC (for example,memory cells of the same type used in FLASH memories, formed offloating-gate MOS transistors), which are used instead of the fusiblelinks FL of the first embodiment.

The non-volatile memory cells MC are electrically programmable to storethe binary code, corresponding to the desired radio communicationfrequencies to be used for wirelessly communicating with the die 105. Amemory cell MC that is programmed to store a logic “1” has typically alow threshold voltage, so that, when biased for reading its content, itis conductive; the corresponding bit of the binary code is thus a “1”;conversely, a memory cell MC that is programmed to store a logic “0” hasa relatively high threshold voltage, so that, when biased for readingits content, it is not conductive; the corresponding bit of the binarycode is thus a “0”.

The data for programming the memory cells MC may be received from thetest equipment wirelessly, using the transceiver circuits 165 and 175.

Referring to FIG. 4, an exemplary scheme of a transceiver circuit 175adapted to cooperate with the radio frequency selector 185 according toan embodiment of the present invention is shown. As mentioned above, inan embodiment of the present invention the group of output voltages Voutof the different branches of the frequency selector 185 forms a binarycode, which is adapted for setting the radio communication frequency ofthe transceiver circuit 175. For this purpose, the transceiver circuit175 comprises an oscillator circuit 410 (for example implemented by aColpits oscillator, a ring oscillator, or the like, the type ofoscillator being not limitative) and all the electronic circuits (suchas a modulator circuit 415 and an amplifier circuit 420) which, duringthe test of semiconductor wafer 110, cooperate with the oscillatorcircuit 410 to decode the test signals.

More in detail, the oscillator circuit 410 comprises an oscillator core425, which has an input terminal IN connected to a first terminal of acapacitor C having a second terminal connected to ground. The oscillatorcircuit 410 also comprises a plurality of auxiliary capacitors C1 . . .Cn (for example, n=2) each of which is coupled to the input terminal INof the oscillator core 425 by means of a respective switch SW1 . . .SWn. In detail, each auxiliary capacitor Ci has a first terminal, whichis connected to a first terminal of the corresponding switch SWi, and asecond terminal receiving the ground. Each switch SWi has a secondterminal coupled to the input terminal IN of the oscillator core 425. Inthe example at issue, each switch SWi is enabled by a corresponding oneof the groups of output voltages Vout. In other words, when the outputvoltage Vout is at the supply voltage the first switch SW1 is closed,vice versa when the output voltage Vout is at the ground, the switch SWiis open. In such a way, one or more of the plurality of auxiliarycapacitors Ci (for i=0 . . . n) can be selectively connected in parallelto the capacitor C by means of the corresponding switches SWi, so thateach auxiliary capacitor Ci increases an equivalent capacitance which isconnected to the input terminal of the oscillator core 425 (when thecorresponding switch SWi is closed).

Depending on the binary code stored in the frequency selector, the radiocommunication frequency of the generic transceiver circuit 175 is thusaccordingly set, since the radio communication frequency depends on theequivalent capacitor which is connected to the input terminal IN of theoscillator core 425.

Alternatively, according to a third embodiment of the present invention,the switches SWi may be directly implemented as fusible links. In suchway, the radio communication frequency can be set in each transceivercircuit 175 by selectively burning the fusible links.

In detail, after manufacturing of the wafer 110 the fusible links areconductive so that each capacitor Ci is connected in parallel to thecapacitor C. During the programming phase of the radio communicationfrequency of each transceiver circuit, one or more fusible links can beburned, becoming essentially an open circuit, thereby disconnecting thecorresponding capacitor Ci from the capacitor C. In such a way, theequivalent capacitance which is connected to the oscillator core 425 isreduced so setting the desired radio communication frequency.

According to a further embodiment of the present invention, fordifferentiating the radio communication frequencies of each die 105 ofthe wafer 110, or of at least of groups of two or more adjacent dies onthe wafer, it is possible to deliberately introduce chip-to-chipvariations in the pattern of, e.g., metal lines formed in the IC. Forexample, each transceiver circuit 175, and more in particular eachoscillator circuit 410 is designed so that it can wirelessly communicateto the corresponding wireless unit 140 on the wireless probe card 125with a proper predetermined radio communication frequency. This can beaccomplished by modifying (for example, adding contact vias) fromchip-to-chip the metal lines connecting the auxiliary capacitors to thecapacitor C.

Finally, in FIG. 5 a cross-sectional view of test equipment 500 isschematically shown, in which an exemplary structure and the positioningof the wireless probe card 125 and of the semiconductor wafer 110 to betested is visible.

The semiconductor wafer 110 is placed on a chuck 505, which is capableof movement in the three orthogonal directions “x”, “y” and “z”. Thechuck 505 may also be rotated and tilted, and it may be further capableof other motions, so that once that the semiconductor wafer 110 isplaced on the chuck 505, the latter is moved so that the dies 105 arebrought close to the wireless probe card 125, for enabling the wirelesscommunication therewith.

In the example at issue, the wireless probe card 125, in one of itspossible embodiment, includes a PCB 510 (for example, comprising thecontrol circuit 130, the storage unit 160 and the tester input/outputinterface 150) forming a support for a silicon wafer 520 wherein thetransceiver circuits 165 are formed. The antennas 170 are embedded in aglass wafer 525, which is placed in contact with the silicon wafer 520so that the antennas 170 are coupled to the transceiver circuit 165.These antennas 170 (and 180) can be inductors or capacitor plates, or acombination thereof. For example, the antennas 170 (and 180) can beimplemented by metal traces having dimensions that can depend on usedprocess technologies and design choices because it's possible to supplypower to die 105 using electromagnetic waves or using standard methods.

A top view of the wireless probe card 125 (including the silicon wafer520 and the glass wafer 525 wherein the transceivers 165 and theantennas 170 are respectively embedded) and the semiconductor wafer 110is also shown in the drawing.

The antennas 170 are positioned within the glass wafer 525 to form atwo-dimensional arrangement which corresponds to the arrangement of dies105 on the semiconductor wafer 110 under test.

The antennas 170 (and 180) can have same or similar size or differentsizes, in agreement with the different used frequencies and designchoices.

Fiducial images 530 can be provided on the PCB 510 for allowing thecorrect alignment between the wireless probe card 125 and thesemiconductor wafer 110.

The present invention allows testing at the same time the wholesemiconductor wafer 110, or at least of groups of adjacent dies. Indeed,no cross talk phenomena occurs when the test is performed since theradio communication frequencies used to communicate with each die 105under teste are different from the radio communication frequencies usedfor communicating with the other dies 105 under test, for exampleadjacent dies.

In this way, a significant reduction of the test time is obtained socausing a productivity improvement, as well.

Moreover, since the test is wirelessly performed and the mechanicalprobes are (fully or at least in part) eliminated, it is possible toreduce the pad area of the dies so obtaining a significant reduction ofthe whole area of the die.

In addition, the present invention has the typical advantages ofwireless testing, particularly mechanical problems due to the presenceof a large number of probes are eliminated by using the wirelesscommunication according to the present invention.

Moreover, the wireless test system according to the present invention issignificantly less expensive than those using mechanical probes.

Naturally, in order to satisfy local and specific requirements, a personskilled in the art may apply to the solution described above manymodifications and alterations. Particularly, although the presentinvention has been described with reference to preferred embodimentsthereof, it should be understood that various omissions, substitutionsand changes in the form and details as well as other embodiments arepossible; moreover, it is expressly intended that specific elementsand/or method steps described in connection with any disclosedembodiment of the invention may be incorporated in any other embodimentas a general matter of design choice.

For example, although in the preceding description reference has beenmade to a test system wherein the non volatile storage comprises memorycells of flash type, memory cells of different type (such as EEPROMtype) or arranged with a different architecture (for example, of NANDtype) can be used.

Having thus described at least one illustrative embodiment of theinvention, various alterations, modifications, and improvements willreadily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be within the spirit andscope of the invention. Accordingly, the foregoing description is by wayof example only and is not intended as limiting. The invention islimited only as defined in the following claims and the equivalentsthereto.

What is claimed is:
 1. An apparatus, comprising: a wireless probe cardhaving a plurality of wireless units, the plurality of wireless unitsincluding at least a first wireless unit and a second wireless unit,wherein the first wireless unit is configured to wirelessly communicatewith a first integrated circuit die from among a plurality of integratedcircuit dies at a first frequency, the first integrated circuit diebeing integrated within a single wafer and including a radio frequencyselector configured to select the first frequency for use by the firstintegrated circuit die from among a plurality of radio frequencies,wherein the second wireless unit is configured to wirelessly communicatewith a second integrated circuit die from among the plurality ofintegrated circuit dies at a second frequency different than the firstfrequency, the second integrated circuit die being integrated within thesingle wafer and including a radio frequency selector configured toselect the second frequency for use by the second integrated circuitfrom among a plurality of radio frequencies, wherein the plurality ofwireless units are at least equal in number to a number of theintegrated circuit dies integrated within the single wafer.
 2. Theapparatus of claim 1, wherein each wireless unit of the plurality ofwireless units of the wireless probe card is configured to wirelesslycommunicate with a respective integrated circuit die at a respectivefrequency.
 3. The apparatus of claim 1, wherein the wireless probe cardfurther comprises a control circuit configured to manage test signalsexchanged between the wireless probe card and a tester.
 4. The apparatusof claim 3, further comprising the tester.
 5. The apparatus of claim 1,wherein the first wireless unit comprises a first transceiver ortransponder circuit configured to transmit wireless signals at the firstfrequency.
 6. The apparatus of claim 5, wherein the first transceiver ortransponder circuit is physically coupled to a first antenna on thewireless probe card.
 7. The apparatus of claim 1, further comprising atester coupled to the wireless probe card.
 8. The apparatus of claim 1,wherein the first wireless unit communicates with the first integratedcircuit die at the first frequency by communicating with a firsttransceiver or transponder integrated within the first integratedcircuit die for testing a first integrated circuit also integratedwithin the first integrated circuit die; and wherein the second wirelessunit communicates with the second integrated circuit die at the secondfrequency by communicating with a second transceiver or transponderintegrated within the second integrated circuit die for testing a secondintegrated circuit also integrated within the second integrated circuitdie.
 9. The apparatus of claim 1, wherein the plurality of wirelessunits further includes a third wireless unit; and wherein the thirdwireless unit is configured to wireless communicate with a thirdintegrated circuit die of said single wafer at a third frequencydifferent than the second frequency.
 10. An apparatus, comprising: awireless probe card having a plurality of wireless units, wherein eachwireless unit of the plurality of wireless units is configured towirelessly communicate with a different integrated circuit die of aplurality of integrated circuit dies included within a given wafer at agiven frequency different than a frequency used by adjacent wirelessunits of the plurality of wireless units to communicate with otherintegrated circuit die of the given wafer, with each of the plurality ofintegrated circuit dies includes a radio frequency selector configuredto select the given frequency for use by that integrated circuit diefrom among a plurality of radio frequencies; wherein the plurality ofwireless units are at least equal in number to a number of theintegrated circuit dies included within the given wafer.
 11. Theapparatus of claim 10, wherein each wireless unit of the plurality ofwireless units is configured to wirelessly communicate with a differentintegrated circuit die included within the given wafer at a frequencydifferent than a frequency used by other wireless units of the pluralityof wireless units.